Method for stripping sacrificial layer in MEMS assembly

ABSTRACT

The present invention provides methods of manufacturing a MEMS assembly. In one embodiment, the method includes mounting a MEMS device, such as a MEMS mirror array, on an assembly substrate, where the MEMS device has a sacrificial layer over components formed therein. The method also includes coupling an assembly lid to the assembly substrate and over the MEMS device to create an interior of the MEMS assembly housing the MEMS device, whereby the coupling maintains an opening to the interior of the MEMS assembly. Furthermore, the method includes removing the sacrificial layer through the opening. A MEMS assembly constructed according to a process of the present invention is also disclosed.

TECHNICAL FIELD OF THE INVENTION

[0001] Disclosed embodiments herein relate generally to microelectro-mechanical systems (MEMS) assemblies, and, more specifically, tomethods for stripping a sacrificial layer from MEMS devices during themanufacturing process.

BACKGROUND OF THE INVENTION

[0002] Optoelectronic devices have continued to gain popularity withtoday's top manufacturers. Specifically, micro electromechanicaldevices, such as actuators, motors, sensors, and micro electromechanicalsystems (MEMS), such as spatial light modulators (SLMs), are some of thefew types of optoelectronic devices gaining in use. Such packaged SLMsand other types of MEMS devices are employable in “digital micro-mirrordevice” (DMD) technology, of the type designed and used by TexasInstruments of Dallas, Tex.

[0003] Such DMD MEMS assemblies include arrays of electronicallyaddressable mirror elements (or “pixels”), which are selectively movableor deformable. Each mirror element is movable in response to anelectrical input to an integrated addressing circuit formedmonolithically with the addressable mirror elements in a commonsubstrate. Such MEMS assemblies modulate incident light in a spatialpattern, pursuant to an electrical or other input, in phase, intensity,polarization or direction. The incident light is modulated by reflectionfrom each mirror element.

[0004] Unfortunately, defects may be caused by contamination of the MEMSmirror array during various stages of the manufacturing process. Forexample, at certain points, the MEMS array may be stripped of anyprotective layer, exposing the MEMS array to contaminates before it issealed within the MEMS assembly. More particularly, contaminants, oftenin the form of debris particles, may contaminate the mirror array duringthe wafer saw process, array mounting stage, wire-bonding processes, andeven the during the final assembly stage for the MEMS assembly. Suchcontamination may detrimentally affect the function of the mirror, andas the number of defects increases, so too does the overallmanufacturing costs due to decreased wafer yield.

BRIEF SUMMARY OF THE INVENTION

[0005] Embodiments described in this application provide methods ofmanufacturing a MEMS assembly that protects the MEMS devices fromcontamination. In one embodiment, the method includes mounting a MEMSdevice, such as a MEMS mirror array, on an assembly substrate, where theMEMS device has a sacrificial layer over and/or under components formedtherein. The method also includes coupling an assembly lid to theassembly substrate and over the MEMS device to create an interior of theMEMS assembly housing the MEMS device, whereby the coupling maintains anopening to the interior of the MEMS assembly. The method furtherincludes removing the sacrificial layer through the opening.

[0006] In another aspect, described methods provide for a MEMS assemblyconstructed by mounting a MEMS device on an assembly substrate, wherethe MEMS device has a sacrificial layer over components formed on it.The exemplary process includes the coupling of an assembly lid to theassembly substrate and over the MEMS device to create an interior of theMEMS assembly that houses the MEMS device, whereby the couplingmaintains an opening to the interior of the MEMS assembly. In thisembodiment, the MEMS assembly is further constructed by removing thesacrificial layer through the opening.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a more complete understanding of the present invention,reference is now made to the following detailed description taken inconjunction with the accompanying drawings. It is emphasized thatvarious features may not be drawn to scale. In fact, the dimensions ofvarious features may be arbitrarily increased or reduced for clarity ofdiscussion. Reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

[0008]FIG. 1 illustrates an isometric view of one embodiment of a MEMSarray that could be incorporated in MEMS assemblies of the presentinvention;

[0009]FIG. 2A illustrates a side section view of the MEMS assemblyduring an initial stage of the manufacturing process of the presentinvention;

[0010]FIG. 2B illustrates the MEMS assembly of FIG. 2A during anotherstage in the manufacturing process;

[0011]FIG. 2C illustrates the MEMS assembly later in the manufacturingprocess;

[0012]FIG. 2D illustrates the completed MEMS assembly, as constructedaccording to the principles of the present invention;

[0013]FIG. 3 illustrates a side section view of another embodiment of aMEMS assembly, constructed according to the principles of the presentinvention; and

[0014]FIG. 4 illustrates a flow diagram of one embodiment of a methodfor manufacturing MEMS assemblies employing the techniques of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Referring initially to FIG. 1, illustrated is an isometric viewof one embodiment of a micro electromechanical system (MEMS) mirrorarray 100. The illustrated MEMS mirror array 100 includes asemiconductor substrate 105 on which a plurality of MEMS mirrors 110, aswell as other associated components, are formed. The MEMS array 100 mayhave, for example, several hundred, thousand, or even hundreds ofthousands, of mirrors 110 formed thereon. Examples of MEMS structuresand manufacturing methods have been developed and described by TexasInstruments of Dallas, Tex., including “digital micro-mirror device”(DMD) technology.

[0016] In function, the mirrors 110 formed on the MEMS array 100 reflectbeams of light, therefore modulating the light, by moving or rotating onone or more relatively thin, integral supporting beams or hinges.Depending on the type of beams or hinges formed, the mirrors 110 may bea cantilever design or may be supported by one or more torsion beams orflexure beams, depending on the desired application. Deflection of eachmirror 110 is effected by the attractive electrostatic force exerted ona portion of the mirrors 110 by an electrical field resulting from apotential applied to an associated control electrode located beneatheach of the mirrors 110 and formed on the substrate 105. The potentialis selectively applied to the control electrode by an addressing circuitformed in the semiconductor substrate 105 beneath the mirrors 110.

[0017] When a mirror 110 is deflected to a first position according to avoltage applied to the control electrodes by the addressing circuit, themirror 110 reflects light along a first path to a first site. However,when the addressing circuit applies a different voltage to theunderlying electrodes, the mirror 110 is electrostatically attracted toa second position whereby it reflects light along a second path,different from the first path, thus redirecting the light to a differentsite. From the foregoing, the incident light is modulated by the mirrors110 in the MEMS array 100 so that it selectively reaches the first orsecond site, whichever contains the desired target of the beam of light.

[0018] Turning now to FIGS. 2A-2D, illustrated are side section views ofa MEMS assembly 200 throughout various stages of a manufacturing processaccording to the principles disclosed herein. More specifically,beginning with FIG. 2A, illustrated is the MEMS assembly 200 during aninitial stage of one embodiment of a manufacturing process. The MEMSassembly 200 includes an assembly substrate 205 on which a MEMS device,in this example a MEMS mirror array 210, is shown being mounted. Asdiscussed above, the MEMS array 210 includes a plurality of mirrors 215for modulating an incoming beam or beams of light in the mannerdescribed above.

[0019] Also as shown in FIG. 2A, the MEMS array 210 includes asacrificial protective layer 220 formed thereon. Among other things, theprotective layer 220 provides protection for the mirrors 215 fromcontaminants that otherwise reach the MEMS array 210. If contaminantsare allowed to reach and affect the MEMS array 210, the yield of gooddevices from the wafer from which the MEMS array 210 was cut potentiallydecreases. The protective layer 220 may be blanket-deposited over theMEMS array 210 while it is still joined with other arrays to form thesemiconductor wafer. In one embodiment, the protective layer 220 is aphotoresist, but other types of protective layers 220 may also beemployed.

[0020] Looking now at FIG. 2B, illustrated is the MEMS assembly 200 ofFIG. 2A during another stage in the manufacturing process. Specifically,an assembly lid 225, having a window 230 for incident light to passthrough and reach the MEMS array 210, is shown being mounted onto theassembly substrate 205 and over the MEMS array 210. The mounting of thelid 225 creates an interior of the MEMS assembly 200, in which the MEMSarray 210 is now located. However, removing the protective layer 220from the MEMS array 210 before the assembly lid 225 is coupled to thesubstrate 205 would leave the MEMS array 210 exposed to potentialcontaminants. As a result, the process of the present invention providesfor the coupling of the assembly lid 225 to the substrate 205 prior tothe removal of the protective layer 220.

[0021] Referring now to FIG. 2C, illustrated is the MEMS assembly 200later in the manufacturing process. As illustrated, the assembly lid 225has been coupled or affixed to the assembly substrate 205. Specifically,in this embodiment, the assembly lid 225 has been tack-welded to thesubstrate 205, as shown by the tack-weld bead 235 on the right side ofthe MEMS assembly 200. Since the assembly lid 225 has only beentack-welded to the assembly substrate 205, openings or vents 240 remainalong different portions of the MEMS assembly 200, where the lid 225 andthe substrate 205 meet but are not welded. Other techniques for leavingsuch openings 240 include applying a non-continuous bead of adhesivebetween the substrate 205 and the lid 225. Although only one opening 240is illustrated in FIGS. 2A-2D, several openings 240 between the assemblylid 225 and the assembly substrate 205 may be prevalent, for example,via the spaces between multiple tack welds, until the two arepermanently sealed together towards the end of the manufacturingprocess.

[0022] Once the MEMS assembly 200 is tack-welded, or otherwise partiallycoupled together, the entire assembly may be moved to a differentstation that has pressurizing capabilities. Alternatively, the MEMSassembly 200 may be entirely or substantially manufactured in such alocation. In yet another embodiment, when pressurizing is not requiredor desired, the MEMS assembly 200 may be manufactured at any appropriatestation, perhaps already present in conventional manufacturingprocesses.

[0023] Still referring to FIG. 2C, a removing material, for example, agas or fluid, is then introduced into the interior of the MEMS assembly200, and used to remove or strip the protective layer 220 covering theMEMS array 210. The insertion of the removal fluid or other removingmaterial is indicated by arrows A₁. In one embodiment, a supercritical“fluid,” such as highly pressurized carbon dioxide (CO₂) at temperaturesgreater than 31° C. and pressures greater than 1070 psia, may be used toremove the protective layer 220. In a related embodiment, the removalprocess with the supercritical material may be repeated several times toinsure that all of the protective layer 220 is removed from the MEMSassembly 200 and flushed through the opening 240. In such embodiments,once the supercritical material has entered the interior of the MEMSassembly 200 and dissolved the protective layer 220, the ambientpressure surrounding the MEMS assembly 200 may be reduced, causing thesupercritical fluid to be evaporated from the MEMS assembly 200, takingthe dissolved protective layer 220 with it through the opening 240.

[0024] In other embodiments, other materials may be used to strip awaythe protective layer 220, including but not limited to a solvent, suchas acetone. By using a supercritical fluid, or other fluid or materialcapable of stripping the protective layer 220 from the MEMS array 210,the material may penetrate not only the protective layer 220 over themirrors 215, but also around and underneath the mirrors 215, as well asother components found on the MEMS array 210 in order to remove theprotective layer 220 from all of those areas and permit the MEMSassembly 200 to function properly.

[0025] Turning now to FIG. 2D, illustrated is the completed MEMSassembly 200, as constructed according to the principles of the presentinvention. After the removing material is used to remove the protectivelayer 220, a passivation or lubrication step may be conducted. Morespecifically, many types of MEMS assemblies perform best with some typeof lubrication around the parts of the MEMS array 210 so as to mitigateor prevent sticking of the mirrors to electrodes, or other similarproblems that may affect device performance. In addition, the MEMS array210 may perform well over longer periods of time if passivated toprovide protection to its components. As such, the illustratedembodiment provides an opportunity to mix a lubricant or passivant intothe ambient 245 of the interior of the MEMS assembly 200. For example, apassivation material, such as perflourodecanoic acid (PFDA), may beintroduced into the interior to reach all the necessary placessurrounding the MEMS array 210, as indicated by arrows A₂. Such anapproach is set forth in commonly assigned co-pending patent applicationserial #______, and entitled “Method for Lubricating or Passivating MEMSComponents” (Attorney Docket #24154816.24), which is incorporated hereinby reference.

[0026] In addition, the final ambient 245 may be selected and introducedbefore the opening 240 is sealed. For example, if a nitrogen-basedambient 245 is desired for the MEMS assembly 200, a nitrogen-rich gasmay be introduced into the interior of the assembly 200. With thisadditional step, the ambient 245 of the MEMS assembly 200 may bespecifically selected depending on the intended application of theassembly 200. Additionally, flushing the ambient 245 in this manner maybe useful in removing any residual traces of the removal fluid used tostrip the sacrificial protective layer 220. Other gases or liquids ofvarying viscosity or other characteristics may be introduced, as well.Moreover, a specific ambient 245 may be introduced into the interior,and then later flushed, if beneficial to particular applications. Ofcourse, no specific ambient 245 is required to practice the presentinvention, or the ambient 245 may comprise any elements or compoundswithout deviating from the scope of the invention disclosed herein.

[0027] After removal of the protective layer 220, the opening 240 issealed to further protect the MEMS array 210, as well as othercomponents that may be located in the interior of the MEMS assembly 200.In one embodiment, the opening 240 may be sealed by seam-welding 250around the entire surface where the assembly lid 225 meets the assemblysubstrate 205. Of course, other techniques for sealing any openings 240between the two may also be employed to advantage. For example, epoxy orother curable fillers or adhesives may be used to form a seal or tocompletely enclose the assembly 200. Additionally, a plug may be used toseal the opening 240. The resulting enclosed cavity may be hermeticallysealed or not.

[0028] Looking now at FIG. 3, illustrated is a side section view ofanother embodiment of a MEMS assembly 300. As shown, the MEMS assembly300 also includes an assembly substrate 305 on which a MEMS array 310having a plurality of micro-mirrors 315 is mounted. Covering the MEMSarray 310 is also a protective layer 320, such as photoresist or otherappropriate material. Once the MEMS array 310 is mounted, an assemblylid 325, having a window 330 for incident light to pass through, iscoupled to the assembly substrate 305 and over the MEMS array 310.

[0029] However, in this embodiment, the assembly lid 325 is completelysealed to the assembly substrate 305 prior to the removal of theprotective layer 320. As before, the lid 325 may be sealed to thesubstrate 305 using, for example, seam-welding 335 between the two. Ofcourse, other techniques to couple to two together may also be employed.Although the lid 325 has been sealed to the substrate 305, an opening340 has been incorporated into the assembly substrate 305 for thepurpose of stripping the protective layer 320 from the MEMS array 310 inthe manner disclosed herein. Alternatively, the opening 340 may beincorporated into the lid 325. Thus, like the opening 240 illustrated inFIG. 2C, the opening 340 in FIG. 3 may be used to introduce a removingfluid or compound into the interior of the MEMS assembly 300 todissolve, and thereby remove, the protective layer 320 from the MEMSarray 310 through the opening 340, allowing it to function as intended,without the risk of contamination or other type of damage to the MEMSarray 310 typically present during conventional manufacturing processes.This opening 340 could then be sealed after the removal of theprotective layer 320 using one of the techniques described above, or anyother available technique.

[0030] Turning finally to FIG. 4, illustrated is a flow diagram 400 ofone embodiment of a method for manufacturing MEMS assemblies, such asthe assemblies described above, employing the techniques disclosedherein. The method begins at a start block 405 where any initialmanufacturing steps not directly associated with the principlesdisclosed herein are performed on the MEMS assembly. For example, thesteps employed to manufacture the MEMS array on a semiconductor wafermay be performed in this initial stage of manufacturing.

[0031] At block 410, a semiconductor wafer on which multiple MEMS arrayshave been formed is sawed into individual arrays. Prior to sawing, theentire wafer is covered with a protective layer, such as the photoresistdescribed above, to protect the MEMS arrays from contaminants, as wellas physical, damage during other stages of manufacturing. Knownsingulation techniques may be used to saw the wafer into the individualarrays.

[0032] As the process moves to block 415, an individual MEMS array, cutfrom the wafer, is mounted onto an assembly substrate. In particular,traces and contact pads associated with the MEMS array are aligned withassociated traces and contact pads formed on the assembly substrate. Atblock 420, wire-bonding is employed to electrically couple thosecontacts of the MEMS array to the contacts of the assembly substrate.Employable wire-bonding techniques are widely known, and any suchtechnique may be employed with the present process.

[0033] Moving on to block 425, the assembly lid is tack-welded to theassembly substrate, to partially couple the two together and create aninterior of the MEMS assembly in which the MEMS array is located. Byonly partially coupling the two together, openings between individualtack-welds remain, through which removal fluids may be forced orotherwise introduced into the interior of the MEMS assembly. At block430, a supercritical material is introduced into the interior of theMEMS assembly. The supercritical material is used to dissolve theprotective layer, as indicated in block 435, and to remove theprotective layer from over and around the MEMS array through theopening(s). As discussed above, the lid and substrate may be completelywelded together at block 425 of the process, causing a hermetic, orother appropriate, seal between the two. In such an embodiment, anopening(s), other than one associated with tack-welds between the lidand substrate, is engineered into the substrate or lid. This opening maythen be used to introduce supercritical fluid or other material into theinterior of the MEMS assembly, at block 430, to strip the protectivelayer from the MEMS array.

[0034] Also as discussed above, in another embodiment, the removal fluidneed not be a supercritical fluid, but may instead be a solvent or anytype of removal fluid capable of removing the protective layer throughthe opening(s) without excessive damage to the MEMS array. In suchembodiments, the solvent not only removes the protective layer, but mayalso help clean various surfaces within the interior of the MEMSassembly. In yet another embodiment, a supercritical fluid may first beused to dissolve and remove the protective layer, and then a solvent maybe employed to clean-up surfaces after the removal. In a relatedembodiment, the MEMS assembly may be baked after using the solvent inorder to help release structures within the MEMS array held by capillarystiction, which often cause certain components of the MEMS array tostick together as a result of the drying stage of the cleaning process.In yet another embodiment, a solvent may first be employed to remove theprotective layer, and then a supercritical fluid may be employed toclean-up residual solvent or particles of the protective layer, and tohelp release structures held by capillary stiction. Moreover, in any orall of such exemplary embodiments, the protective layer may bespecifically engineered from specific elements or compounds for easyremoval with certain supercritical fluids or solvents, thus furtherimproving the manufacturing process.

[0035] Once the protective layer is stripped from on and around the MEMSarray, the process moves to block 440 where the option to passivateand/or lubricate the components within the MEMS assembly, primarily theMEMS array, is presented. If desired, a passivant or lubricant may beintroduced through the opening(s) in the MEMS assembly and permitted toinfiltrate all areas of its interior. In addition, in embodiments wherea getter is formed in the interior of the MEMS assembly, the opening maybe employed in this manner to activate the getter to provide lubricationor passivation to the components within the MEMS assembly over the lifeof the assembly. However, such coating through the opening(s), or at anystage of the manufacturing process, may be employed or not employed inthe methods disclosed in this application. For a more detaileddiscussion on getter formation in MEMS assemblies, see U.S. Pat. No.5,610,438, entitled “Micro-Mechanical Device with Non-EvaporableGetter”, commonly assigned with the present application, andincorporated herein by reference.

[0036] At block 445, the opening(s) in the MEMS assembly is filled orotherwise sealed. By sealing the opening(s), the interior of the MEMSassembly is protected from external contaminants. In addition, bysealing the opening(s), the ambient of the interior of the MEMS assemblymay be maintained if desired, depending on the particular application.Once the opening(s) is sealed, the process ends at block 450, and theMEMS assembly may then be mounted to a larger DMD device, or otherwiseput into operation for its intended application.

[0037] By employing any process following the principles disclosedherein, such as those described above with reference to the MEMSassemblies 200, 300 and the exemplary process in FIG. 4, MEMSassemblies, and manufacturing processes for the MEMS assemblies, havingsignificant advantages over those found in the prior art, and producedusing conventional techniques, may be manufactured. Specifically, byallowing the protective layer to remain on and around the MEMS arrayuntil after the MEMS assembly is coupled together, the MEMS arraytherein is not left exposed during various early stages of manufactureof the assembly. For example, the protective layer may remain over theMEMS array before, during, and after the removal of the sacrificiallayer. Among conventional techniques, the MEMS array is exposed at thisstage of the process to potential contamination from the handling,processing, and staging environments. In addition, the process describedmay provide protection from contamination during the wire-bonding stageof manufacture. In such an embodiment, it may be necessary to removeportions of the protective layer covering the bonding pads prior toenclosing the MEMS array. Once these portions are removed, the bond padson the MEMS array are exposed and may be wire-bonded to bond padslocated on the MEMS substrate. In this embodiment, the remainingportions of the protective layer provide substantial protection fromdebris potentially generated during the wire-bonding process to criticalcomponents of the MEMS array. Moreover, since the protective layer isstill present at mounting, there is no need to expose the MEMS array inorder to passivate early in the manufacturing process. Furthermore,debris or contaminants from the tack-welding process cannot reach theMEMS array, since the protective layer remains in place during theassembly of the MEMS assembly.

[0038] Thus, by reducing the overall exposure time of the MEMS array, aswell as other components typically protected by the protective layer,during most of the manufacturing process, the overall risk ofcontaminants affecting the performance of the MEMS array, or even thechance of human contact with the MEMS array, is reduced or eveneliminated. Reducing array contamination results in higher wafer yield,thus reducing overall manufacturing costs by producing a greater numberof functional MEMS assemblies per wafer. In addition, in many cases, thedisclosed processes involve fewer steps than conventional processes, yetyielding better results. Moreover, the disclosed processes may beincorporated into existing manufacturing processes since mostly standardmaterials and associated processing steps are employed. Furthermore,such incorporation is possible into almost any type of process, whilestill maintaining benefits such as those described above.

[0039] While various embodiments of an MEMS assembly constructedaccording to the principles disclosed herein, have been described above,it should be understood that they have been presented by way of exampleonly, and not limitation. Thus, the breadth and scope of theinvention(s) should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents. Moreover, the above advantagesand features are effected in described embodiments, but shall not limitthe application of the claims to processes and structures accomplishingany or all of the above advantages. It should also be noted that thedisclosed principles are not limited merely to the manufacture of a MEMSassembly for use in SLMs and the like. In fact, the disclosed processes,and variations, may be employed in the manufacture of non-mirror basedMEMS devices, which may lack windows in the assembly lid discussedabove. Moreover, any device having delicate moveable components maybenefit from use of the principles disclosed herein.

[0040] Additionally, the section headings herein are provided forconsistency with the suggestions under 37 CFR 1.77 or otherwise toprovide organizational cues. These headings shall not limit orcharacterize the invention(s) set out in any claims that may issue fromthis disclosure. Specifically and by way of example, although theheadings refer to a “Technical Field of the Invention,” the claimsshould not be limited by the language chosen under this heading todescribe the so-called field of the invention. Further, a description ofa technology in the “Background of the Invention” is not to be construedas an admission that technology is prior art to any invention(s) in thisdisclosure. Neither is the “Brief Summary of the Invention” to beconsidered as a characterization of the invention(s) set forth in theclaims set forth herein. Furthermore, the reference in these headings,or elsewhere in this disclosure, to “invention” in the singular shouldnot be used to argue that there is only a single point of noveltyclaimed in this disclosure. Multiple inventions may be set forthaccording to the limitations of the multiple claims associated with thisdisclosure, and the claims accordingly define the invention(s) that areprotected thereby. In all instances, the scope of the claims shall beconsidered on their own merits in light of the specification, but shouldnot be constrained by the headings set forth herein.

What is claimed is:
 1. A method of manufacturing a MEMS assembly,comprising: mounting a MEMS device on an assembly substrate, the MEMSdevice having a sacrificial layer; coupling an assembly lid to theassembly substrate and over the MEMS device to create an interior of theMEMS assembly housing the MEMS device, the coupling maintaining anopening to the interior of the MEMS assembly; and removing thesacrificial layer through the opening.
 2. A method according to claim 1,wherein the sacrificial layer is a protective photoresist.
 3. A methodaccording to claim 1, wherein the coupling comprises tack-welding.
 4. Amethod according to claim 3, wherein the opening comprises spacesbetween tack-welding beads formed during the tack-welding.
 5. A methodaccording to claim 1, wherein the opening comprises a vent in theassembly substrate.
 6. A method according to claim 1, wherein theremoving comprises removing the sacrificial layer using a supercriticalcompound introduced through the opening.
 7. A method according to claim6, wherein the supercritical compound is compressed CO₂.
 8. A methodaccording to claim 1, further comprising lubricating components formedon the MEMS device by introducing a lubricant through the opening.
 9. Amethod according to claim 1, further comprising sealing the openingafter removing the protective layer.
 10. A method according to claim 1,wherein the mounting includes mounting a MEMS device on an assemblysubstrate by removing portions of the sacrificial layer covering bondpads on the MEMS device, and wire-bonding to the exposed bond pads andto bond pads on the assembly substrate.
 11. A MEMS assembly constructedaccording to a process comprising: mounting a MEMS device on an assemblysubstrate, the MEMS device having a sacrificial layer; coupling anassembly lid to the assembly substrate and over the MEMS device tocreate an interior of the MEMS assembly housing the MEMS device, thecoupling maintaining an opening to the interior of the MEMS assembly;and removing the sacrificial layer through the opening.
 12. A MEMSassembly according to claim 11, wherein the sacrificial layer is aprotective photoresist.
 13. A MEMS assembly according to claim 11,wherein the coupling comprises tack-welding.
 14. A MEMS assemblyaccording to claim 13, wherein the opening comprises spaces betweentack-welding beads formed during the tack-welding.
 15. A MEMS assemblyaccording to claim 11, wherein the opening comprises a vent in theassembly substrate.
 16. A MEMS assembly according to claim 11, whereinthe removing comprises removing the sacrificial layer using asupercritical compound introduced through the opening.
 17. A MEMSassembly according to claim 16, wherein the supercritical compound iscompressed CO₂.
 18. A MEMS assembly according to claim 11, furthercomprising lubricating components formed on the MEMS device byintroducing a lubricant through the opening.
 19. A MEMS assemblyaccording to claim 11, further comprising sealing the opening afterremoving the sacrificial layer.
 20. A MEMS assembly according to claim11, wherein the mounting includes mounting a MEMS device on an assemblysubstrate by removing portions of the sacrificial layer covering bondpads on the MEMS device, and wire-bonding to the exposed bond pads andto bond pads on the assembly substrate.